Risk Assessment

Question 1

Allelic heterogeneity

Answer 1

Different mutations in the same gene/locus which may produce the same phenotype

Question 2

Locus heterogeneity

Answer 2

Mutations in different genes/locus that may cause the same phenotype

Question 3

What best explains how two parents who both have an autosomal recessive disease can have unaffected children

Answer 3

Locus heterogeneity

If the same disease can be caused by different genes, mom could be rr PP and dad could be RR pp and thus they could have children who are RrPp and not express the autosomal recessive disease

Question 4

Variable expressivity

Answer 4

Variation in clinical features (severity) of a genetic disorder between individuals with the same gene alteration

Think dimmer switch (varying degrees)

Question 5

Penetrance

Answer 5

Percentage of people with a given genotype who are affected (have the phenotype of the disease)

Think light switch (all or nothing)

Question 6

Hardy-Weinberg Equilibrium

Answer 6

p^2+2pq+q^2 = 1

p+q=1

p = frequency of (A) allele
q = frequency of (a) allele

p^2 = frequency of AA genotype (dominant homozygote)

2pq = frequency of Aa genotype (hetorozygote)

q^2 = frequency of aa genotype (recessive homozygote)

Question 7

Heterozygote advantage

Answer 7

Condition where the heterozygote genotype has a higher relative fitness than either the dominant homozygote or recessive homozygote genotype

Question 8

X-Inactivation

Answer 8

One X chromosome in females is randomly inactivated. Females are mosaic with respect to X-linked gene expression.

Also known as Lyonization

Question 9

How is mitochondrial DNA (mtDNA) inherited?

Answer 9

It is maternally inherited

Question 10

Allele

Answer 10

One of a pair, or series, of alternative forms of a gene that occur at a given locus in a chromosome

Question 11

Anticipation

Answer 11

The tendency in certain genetic disorders for individuals in successive generations to present at an earlier age and/or with more severe manifestations

Often observed in disorders resulting from trinucleotide repeat mutations that increase in size with each generation

Question 12

Pedigree

Answer 12

Genetic representation of a family tree that diagrams the inheritance of a trait or disease through several generations

Question 13

Proband

Answer 13

The affected individual through whom a family with a genetic disorder is ascertained; may or may not be the consultant (the individual presenting for genetic counseling)

Question 14

Punnett square

Answer 14

A graphical way of discovering all the potential combinations of genotypes that can occur in offspring